I just saw this thread for the first time.  I'm using Chrome on Win10 also and have had this annoying  problem using https://web.vma.vzw.com/vma/web2/Message.do for eons.  NOT the phone app, NOT the pc app, just the website used for messaging.

I type a long text message on that site, press Enter, then in the text box it says "Sending" forever and never actually sends the message.  If I click on the refresh button, the page reloads and my message is gone.

PLEASE FIX THIS ABOMINATION.